This proposal is a plan for carrying out a multicenter randomized clinical trial assigned to assess the efficacy of argon laser trabeculoplasty (ALT) as an alternative to standard medical therapy of open angle glaucoma. The trial will involve the recruitment of 240 patients with newly diagnosed symmetrical open angle glaucoma. Only patients aged 30 or older (of either sex) with intraocular pressures of 27 mm Hg or greater, and evidence of optic nerve damage in both eyes will be eligible for enrollment. The patients will each be followed for a minimum of two years in order to collect information on pressure levels over the course of the trial and to provide comparative data on the rate of vision field loss and increased optic nerve cupping. Treatment groups will be compared at the end of the two years of follow-up with regard to the amount of medical treatment needed to control the intraocular pressure and to determine the usefulness in preventing further nerve damage. If ALT is equal to or better than medicine, efforts will be made to continue, and to possibly expand, the study for five more years to follow the status of the optic nerve in both groups of eyes. The eye to be lasered will be randomly selected. The ALT will consist of 96 burns delivered onto the anterior middle aspect of the trabecular meshwork, avoiding the posterior or uveal meshwork. The burns will be delivered at a suitable intensity to cause blanching of the meshwork just at the threshold of bubble formation (between 700 and 1200 MW per lesion). The fellow eye assigned to medical therapy will be placed on a single topical medication. Eyes requiring added treatment over and above the initial treatment (i.e., laser trabeculoplasty or single topical medical) to control IOP will have subsequent topical medication(s) added in a stepwise fashion according to a protocol. The trial will involve a total of 6 Clinical Centers, a Data Coordinating Center, a Disc Stereophoto Reading Center, and a Visual Field Reading Center.